Hi,
I am a first-year gardener myself 🙂 I understand very well the excitement of a new plan.
I find it difficult to give tips for your specific situation – I cannot count on years of experience. Still, a few comments:
– Perhaps you might want to start with a general plan and make it more specific as you proceed. This gives more breathing space and allows more creativity. Unless you are very sure about what you want, that is.
– I have a slight slant in my garden and do not worry about it a bit, but my soil is sandy and covered with plants. Even with heavy rain, the water disappears instantly. Your situation might be different, and heavy thunderstorms might wash away your top soil. If you fill raised beds with compost, this might be less of a situation. I have not attempted to make my raised beds level, but my situation is rather different.
– Concerning shadow, note that we are currently around the Summer solstice and shadows at noon are at their shortest. At the Winter Solstice, they will be at their longest. Since Vienna is at ~48°N, expect that the length of an object’s shadow at noon is about 0.45 times the object’s height (tan 24.14°), while at equinox it will be about 1.111 times (tan 48°, from 21 March – 21 September). I personally would not make a definitive plan before the end of September, as this will give a better idea about how much shadow you will have and where it will occur. Also, the situation of end September will reoccur in end March/early April, when early growth is in need of the Sun’s energy.
Good luck 🙂